Adds golden-file tests for the new --signing-key-secret and
--signing-key-type flags: no-signing (baseline), default-gpg (asserts
type: gpg is rendered explicitly when only the secret is set), ssh,
and the two validation-error cases. Establishes
cmd/flux/testdata/create_image_update/ for future expansion of this
command's coverage.
Signed-off-by: Hidde Beydals <hidde@hhh.computer>
Hidde Beydals